The surface species of passivated and nonpassivated molybdenum nitride samples and their stability at elevated temperatures have been investigated by temperature-programmed decomposition and temperature-programmed reduction with H-2. Large differences between fresh and passivated Mo2N were found. (i) Two types of NHx adsorbed species remain on the freshly prepared Mo2N. The first type, weakly adsorbed, desorbed at 200-300 degrees C. Another type is strongly bonded NHx on the surface of Mo2N, which decomposed to H-2 and N-2 at 560 degrees C. For passivated Mo2N samples, only weakly adsorbed NHx species are present. (ii) An obvious change in the crystalline phase of fresh Mo2N occurred when it was heated at 850 degrees C in He, while for the passivated Mo2N sample no change was observed. When Mo2N was heated to 1000 degrees C, the resulting solid consisted of beta-Mo2N and metallic Mo. Mo2N is completely reduced to metallic Mo at 880 degrees C in H-2. (iii) The H-2 consumption peak around 470 degrees C for passivated Mo2N samples is attributed to the reduction of the passivating oxygen. It is suggested that the main effect of passivation on fresh Mo nitride is to eliminate most of the NHx and H species strongly bonded on nitride and then forming a protective oxide layer The oxygen incorporated during passivation can be removed by H-2 at a moderate temperature.